Hints
When you don't have your rifle yet and you can only use your gun (like in the first mission) click the right thumbstick to use your binoculars, use the crosshair to aim at the item you plan to shoot, click again to go back to normal view (do it gently so not to change your position) now whip out your gun and shoot, if done correctly you can hit lights from across the room :D

Second one is very handy, when hiding in a room for an alerted guard use your optical camera to view the other room, now when the guard comes to check out the room, he won't be able to open the door because you're using the camera, instead of freaking out and sounding the alarm he'll try a few times and walk away with a "it must be nothing".

Especially the last one looks to be a glitch, now I'll just hope they won't fix em, cuz they're fkn handy :D